A mother board for a bus for connecting many functional boards, such as an I/O board, memory board and CPU board (these boards connected to a motherboard are called "daughter boards") via connectors, and performing communication between these daughter boards are widely used for many industrial equipment including measurement control equipment and medical equipment. The standard for buses used for motherboards have been specified in such industrial standards as the IEEE standard and the ICE standard, and various motherboards for buses, such as a motherboard for a VME BUS and a motherboard for a CPCI BUS conforming to these standards have been commercialized according to the size of the board to be connected and the number of slots.
In such a motherboard for a bus (also called a "backplane" or "backboard"), high frequency control signals flow over a bus line formed on the motherboard. In a recent system, in particular, the number of bits, which is the processing unit of a microcomputer, increased from 16 bits to 32 bits to 64 bits, with control signals increasing in speed and frequency as the reference clock speed increases. As a result, transmitted high frequency signals reflect on the bus line, and this reflection component is superimposed on control signals as noise, interfering with the stable operation of the system. To prevent this in a motherboard for a bus which performs high-speed communication processing, a high-speed Schottky diode array (terminating resistance) is mounted next to the last slot on the bus line to absorb high frequency signals so that reflection noise is not generated on the bus line.
However, mounting the above terminating resistance on a motherboard increases the number of components to be mounted on the motherboard, and as a result, the mounting space of conventional components, such as connectors for board connections, capacitors and terminals, decreases, or the size of the motherboard increases.
A solution to this problem is creating a small board with a terminating resistance in the same way as other daughter boards, and this small board is inserted in the last slot on the motherboard. With this solution, however, a small board with a terminating resistance (termination board) occupies the last slot on the motherboard, which decreases the number of available slots for actual operation.